The present invention relates generally to a coupling arrangement for attaching a working tool or machine or a similar device, such as farm equipment, to a vehicle, such as an agricultural tractor. More particularly, the invention is directed to such a coupling of the three point linkage type having two lower guide members, a substantially U-shaped coupling frame pivotally connected to each of the lower guide members and an upper guide member supported from the U-shaped coupling frame by tension springs, the upper guide member is adjustable to vary its longitudinal length and can be immobilized in various longitudinally extended positions.
Three point linkage couplings for attaching working machines to vehicles such as tractors are generally well known in the art and typically include coupling means at one end for attachment to the vehicle or tractor and releasable attaching devices, such as catch hooks carried on the other end for releasable connection to the working machine. Three point linkages of this type having a coupling frame articulated to the lower guide members and from which the upper guide member is suspended by means of tension springs are also known as disclosed in U.S. Pat. No. 3,791,456. Such prior arrangements, however, merely employ the coupling frame as a means for supporting the upper guide member with respect to the lower guide members so that the upper guide member can be moved up and down jointly with the lower guide members. The task of manipulating the upper and lower guide members into a proper position for connection with the working machine is still a difficult operation even when using the three point linkages which have U-shaped frames for coupling the lower guide members with the upper guide member.
It is accordingly the principle object of the present invention to provide a three point linkage which will facilitate and simplify the operations and maneuvers required for coupling and uncoupling a working machine with a vehicle such as a farm tractor.
A more specific object of the present invention is to provide a three point linkage having an upper guide member the length of which can be automatically adjusted upon approach of the vehicle to the working machine by using the coupling frame, and to provide a means for automatically operating a locking device for a catch hook carried by the upper guide member, in response to vertical movement of the lower guide members.
Other objects, features and advantages, along with the foregoing objects of the present invention will become more apparent from the description of the invention in conjunction with the accompanying drawings to be described more fully hereinafter.